Multication-Induced Disorder in an O3-Type NaNi_0.4Mg_0.1Al_0.1Ti_0.3Sb_0.1O₂ Cathode for Sodium-Ion Batteries

Economical sodium-ion batteries (SIBs) are of great interest in large-scale energy storage applications and play a pivotal role in addressing the ever-increasing energy demand. Here, we designed a cation-disordered SIB cathode formulation with multivalent elements, NaNi_0.4Mg_0.1Al_0.1Ti_0.3Sb_0.1O₂ (NMATSO), which crystallizes in an O3-type layered structure and delivers a reversible capacity of ∼122 mAh/g in the voltage window 2.0–4.0 V. The inclusion of metals with different valencies causes disorderliness within the M–O layer, thereby impeding the Na⁺/vacancy ordering in the Na layer. The elements present in the M–O layer offer advantages, such as Ni involvement in electrochemical redox, high valence Sb stabilizing higher Ni²⁺ and maintaining charge neutrality, and the electrochemically inactive Al, Mg, and Ti, which have higher M–O bond dissociation energy strengthening the structure during charge/discharge, thereby improving the cycling stability and suppressing multiphase transitions. The inclusion of Al, Mg, Ti, and Sb in the cathode formulation would pave the way for the development of advanced SIB cathode materials.